Drill and method of producing printed wiring board

ABSTRACT

A printed wiring board manufacturing method for forming a hole penetrating through a board having an electric conductor layer and forming the electric conductor layer in the hole to make electrical connection, the method including forming a hole that penetrates through the board in accordance with a drill featured in that a blade portion is formed at a distal end and a groove is formed by one stripe, and an occupying rate of a metal at a proximal end of the blade tip of the body is in the range of 40% to 80%; and a curvature radius in an axially vertical direction of a deepest portion of the groove is in the range of 1.50 to 3.50 mm, forming an electric conductor layer in a hole, and forming an electric conductor circuit on a top layer of the board.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. Ser. No. 11/631,946, filed Feb. 2, 2007,the entire contents of which are hereby incorporated by reference. U.S.Ser. No. 11/631,946 is a National Stage of International Application No.PCT/JP2005/12414, filed Jul. 5, 2005, and claims the benefit of priorityunder 35 U.S.C. §119 from Japanese Patent Application Nos. 2004-203718,filed Jul. 9, 2004 and 2005-160137, filed May 31, 2005.

TECHNICAL FIELD

The present invention relates to a drill used for a printed wiringboard. In particular, the present invention relates to a drill for alaminate board having laminated thereon a double-sided copper foil of aresin board that configures a printed wiring board and a method formanufacturing a printed wiring board using the drill.

BACKGROUND ART

A through hole is formed in order to obtain electric conductivity of atop and a bottom of a printed wiring board. As an example thereof, apenetration opening is formed through a double-sided copper platedlaminate board by means of a drill, an electric conductor layer isformed at the opening by means of plating or the like, and etching isapplied as necessary, thereby forming a circuit. In this manner, aprinted wiring board having an electric conductor circuit and enablingelectric conductivity of a top and a bottom is formed. These wiringboards are prepared in plurality, and then, a further multi-layeredprinted wiring board is obtained via a prepreg. Alternatively, while awiring board having a through hole is used as a core, an inter-layeredinsulation layer and an electric conductor layer are formed to obtain amulti-layered printed wiring board.

In recent years, with a growing demand for high density of a printedwiring board, reducing an drilling diameter of a through hole moreremarkably has been discussed.

In order to manufacture a printed wiring board along the above growingdemand, there is a need for a small diameter drill for opening a smalldiameter through hole. Such a small diameter drill is disclosed inUtility Model JP 7-33514 A or JP 2004-82318 A and the like.

According to JP 2004-82318 A, rigidity is enhanced, and good holeprecision is obtained by using a drill having formed thereon a shavingdischarge groove formed in one stripe, the drill having 5/100 or less indiameter with respect to the maximum outer diameter of a blade tipportion.

DISCLOSURE OF THE INVENTION Problem to Be Solved by the Invention

However, in a conventional drill, positional precision of a hole to bedrilled has been lowered due to a change of conditions such as amaterial for a board to be drilled or a drilling condition. Namely, apositional shift from a desired position occurs. In addition, at adrilled inner wall portion, unwanted irregularities have been formed.Therefore, if an electric conductor layer is applied into the displacedopening or the opening formed with irregularities to form a throughhole, electrical connectivity or reliability has been lowered andearlier degradation has occurred if a reliability test such as a heatcycle test or a high temperature placement test is carried out.

In drilling using a drill, in order to enhance processing efficiency, aplurality of printed wiring boards are laminated on each other, and aredrilled at the same time. At the time of simultaneous drillingprocessing, there is a demand for all of the printed wiring boards to bedrilled at the same position and in the same shape, regardless of thenumber of printed wiring boards. On a printed wiring board placed at anupper side a relatively preferable opening can be formed, whereas apositional shift or irregularities has occurred on a printed wiringboard at a lower side.

In addition, if the use frequency of a drill becomes high (the number ofdrilling shots becomes large), for example, there further appears afailure described from when 4500 holes that are the end of service lifehave been drilled by means of a drill to be exchanged when 6000 holeshave been drilled.

Further, as a drilling diameter is reduced, in particular, at the timeof carrying out drilling of an opening diameter of 400 microns or less,the frequency that the failure occurs has increased.

The present invention has been made in order to attain the issuedescribed above. It is an object of the present invention to provide adrill featured in that a positional shift on a drilled hole orirregularities on an internal wall of the drilled hole are not formed.

In addition, it is a still further object of the present invention topropose a drill featured in that, even if the use frequency of the drillis increased, a formed through hole does not cause a failure such as apositional shift and does not degrade electrical connectivity orreliability.

In addition, it is indispensable that, in an electric conductor circuitof a printed wiring board a through hole or a via-hole is reduced indiameter with a demand for the achievement of making fine or higherdensity. Concurrently, it has been discussed that the diameter of thethrough hole to be drilled on the board is reduced by using a drillwhose drilling diameter is reduced more remarkably than conventional(for example, the use of a drill whose drilling diameter is equal to orsmaller than 300 microns or a drill whose drilling diameter is equal toor smaller than 150 microns is also included).

In general, in drilling, with a higher use frequency (drilling a boardone time by a drill is referred to as one shot, and the number of shotsdenotes the use frequency), the drill is worn and torn, and thus, adrill damage (that denotes drill breaks, drill missing, or drilldeformation) or preclusion from forming a hole occurs (for example,irregularities occurs on an internal wall of a drilled hole ordeformation occurs). Therefore, the drill is exchanged in advance when apredetermined number of shots has been reached.

In addition, even with a drill whose specified number of shots has beenreached, as long as the degree of damage is light, regrinding of adistal end portion or the like is applied, whereby the drill can be usedagain, and then, board drilling can be carried out.

However, if the drill is reduced in diameter, the strength of the drillper se is lowered. Therefore, a drill damage is likely to occur, a shapefailure of a through hole formed on the board is likely to occur, and apositional shift of the through hole is likely to occur. As a result,electrical connectivity or reliability is easily lowered.

Further, if the use frequency of these drills becomes high, tendency ofa failure (hole shape failure or positional shift) becomes high, andelectrical connectivity or reliability is easily lowered.

It is a still further object of the present invention to propose a smalldiameter drill featured in that, even if a use frequency is increased, adamage hardly occurs, a formed through hole does not cause a failuresuch as a positional shift, and electrical connectivity or reliabilityis not lowered.

Means for Attaining the Issue(s)

As a result of an utmost study of the Inventor et al, it was foundpreferable to use a drill having formed thereon a distal end bladeportion and a shaving discharge groove of a body, in which the shavingdischarge groove of the body is formed in a continuous one stripe and atorsion angle of the shaving discharge groove is in the range of 30degrees to 50 degrees.

When using the drill whose torsion angle is in the range of 30 degreesto 50 degrees, a positional shift of a through hole is reduced, and inother words, the hole forming precision is improved. In addition, thedrilled shavings are properly discharged, and thus, the drilling is notprecluded by the shavings. Therefore, a printed wiring board having itsexcellent electrical connectivity or reliability can be obtained. Inaddition, the wear and tear of a drill associated with its use can berestricted, and therefore, the usable count can be extended moresignificantly than conventional, and the precision or shape of the holeto be drilled is hardly lowered.

If drilling is precluded by shavings, a positional shift of a holeoccurs or irregularities are formed on an internal wall of the hole.Therefore, electrical connectivity or reliability may be lowered. Suchshavings easily apply an excessive stress to a drill, and thus, the wearand tear of the drill is accelerated.

In the case where the torsion angle is less than 30 degrees or thetorsion angle exceeds 50 degrees, the shavings are hardly discharged.Therefore, the shaving precludes drilling caused by a drill, causes apositional shift of a hole or forms irregularities on the internal wallof the hole, thus degrading electrical connectivity or reliability. Inaddition, the wear and tear of the drill is advanced due to the shavingsthat are not discharged. Accordingly, the drill deteriorates with asmall use frequency.

It is further desirable that the torsion angle be in the range of 35degrees to 45 degrees. In this range, the shavings can be efficientlydischarged regardless of drilling conditions such as a rotationfrequency or a drill advancement speed. Therefore, a failure such ashole positional shifts or irregularities on the internal wall of thehole hardly occurs. In addition, the wear and tear of the drill is smallin amount, and therefore, the dill can be used over a more extendedperiod, and the degradation of the precision of the drilled hole doesnot occur.

The torsion angle indicates an angle at which a body forming a drill anda groove cross each other. That is, this angle denotes an angle formedby a leading edge and a straight line parallel to a drill axis passingthrough one point on this edge.

A groove in the body section is intended to discharge shavings from theboard or the like, and it is desirable that a distal end angle of adistal end blade portion be in the range of 110 degrees to 150 degrees.

As long as the distal end angle is in the above range, a positionalshift hardly occurs, and a desired shape of a hole to be formed isobtained. Even if an opening is drilled while a cupper plated laminateboard is laminated in plurality, the openings are formed at the sameposition and in the same shape on both of the upper side cupper platedlaminate board and the lower side cupper plated laminate board.

In addition, even if the use frequency of the drill is increased,electrical connectivity or reliability of a through hole is hardlylowered.

If the distal end angle of the distal end blade portion is less than 110degrees, irregularities are easily formed on the internal wall of thedrilled hole. If irregularities are subjected todesmear processing, suchirregularities are further accelerated, thus increasing widths of theirregularities. When an electrical conductor layer is applied to thedrilled hole to form a through hole, the thickness of the electricconductor layer may be fluctuated due to such irregularities. Therefore,electrical characteristics (such as impedance or through hole internalresistance value) are lowered.

In addition, if the distal end angle of the distal end blade portionexceeds 150 degrees, a drilled hole is easily displaced from a desiredposition. In particular, when a cupper plated laminate board islaminated in plurality, tendency of a positional shift furtherremarkably appears on the lower cupper plated laminate board. Therefore,when a hole has been formed as a through hole, electrical connectionwith another conductor layer is lowered. In addition, if a reliabilitytest is carried out, deterioration starts at an earlier stage.

It is more desirable that the distal end angle of the distal end bladeportion be in the range between 120 degrees and 140 degrees. This isbecause, in this range, a hole deformation or positional shift hardlyoccurs, in particular.

The distal end angle of the blade portion indicates an angle of a gap inwhich, when a drill is viewed from the distal end, there is no metalportion formed of one blade. This denotes an angle when a cutting bladehas been projected in parallel to a face parallel to the drilling axis.

It is desirable that an angle of a second release angle of a distal endblade portion be in the range of 30 degrees to 50 degrees.

As shown in FIG. 2 (A), a distal end release face of a drill accordingto the present invention is formed in a multi-staged face shape composedof a plurality of flat release faces. First to fourth release faces thatare flat faces from the cutting blade to the drill rotation directionare sequentially disposed along a peripheral direction. Among them, itis desirable that a release angle of the second release face (an angleformed by an axially vertical cross section and a release face at anouter periphery corner) be set in the range of 30 degrees to 50 degrees.

In a drill, it is desirable that a distal end outer diameter of a bladeportion be equal to or smaller than 350 microns.

Having that diameter has an advantage that hole position precision iseasily improved, and the drilled hole is formed in a desired shape.Thus, the lowering of electrical connectivity or reliability hardlyoccurs.

Conversely, if the distal end outer diameter exceeds 350 microns, theshavings to be discharged are increased in size, and thus, the drilledhole position precision is hardly improved. If the outer diameter isequal to or smaller than 50 microns, the drill easily breaks, and laserprocessing has an advantage. Here, it is desirable that the drilldiameter be in the range of 50 microns to 350 microns. In particular, itis preferable that the diameter be in the range of 75 microns to 300microns.

In addition, in a drill equal to or smaller than 100 microns indiameter, drill breakage easily occurs due to even small use frequency,depending on a processing condition. In this case, total thickness atthe time of processing is reduced in accordance with a technique ofdecreasing the thickness of an insulation layer of a board to beprocessed or decreasing the laminate number of boards, thereby making itpossible to enhance a use frequency while ensuring the hole positionprecision as described above.

In a so-called undercut drill, a neck narrowed in a cylindrical shape isformed in a body. A portion from a distal end of this blade portion tothe neck is referred to as a margin portion. It is desirable that ashaving discharge groove formed in the body be defined at the insidewith respect to the end of this margin portion. That is, it ispreferable that the shaving discharge groove should not contact to theneck. In particular, it is desirable that the distance be at the insideby 100 microns or more from the end. In this manner, the discharge ofshavings can be properly carried out, and a stress is not applied. Thus,the degradation of the hole position precision or the shape of a hole tobe formed does not occur.

A length of a margin portion indicates a distance from a distal end to aneck, i.e., a length obtained by subtracting a length of the neck from afull length of a body. It is desirable that the margin portion be in therange of 0.1 mm to 0.3 mm in length. In particular, in the case wherethe distal end outer diameter of a drill is equal to or smaller than 200microns, it is more desirable that the length of the margin portion isin the range of 0.1 mm to 0.3 mm.

If the length of the margin portion is less than 0.1 mm, a region formedby a groove for discharging shavings is reduced, and thus, a stress iseasily applied to a drill. Therefore, the stress cannot be buffered,thus increasing a frequency of an occurrence of drill bending orbreakage and the like. In addition, the hole position precision may belowered.

If the length of the margin portion exceeds 0.3 mm, hole positionprecision is lowered.

An undercut type equipped with a neck is suitable to form a smalldiameter hole. Namely, a hole equal to or smaller than 400 microns canbe drilled. Further, it is preferable to drill a hole equal to orsmaller than 200 microns, in particular.

However, in such an undercut type, if one groove for dischargingshavings is formed, the shavings may be hardly discharged.

Namely, if a position at which the groove is formed contacts to theneck, the shavings are hardly discharged. Thus, an excessive stress isapplied to a drill per se. Therefore, the position precision or thelowering of the shape of a hole to be formed easily occurs.

In the present invention, a drill having a groove formed in a one-stripeshape at a distal end blade portion and at a body in order to form anopening while a work piece is rotated, wherein an occupying rate of ametal at a proximal end of a blade tip of the body is in the range of40% to 80%, and a curvature radius in an axially vertical direction of adeepest portion of a groove at the proximal end is in the range of 1.50mm to 3.50 mm. The distal end diameter of the drill may be equal to orsmaller than 300 microns.

In the present invention, there is provided a printed wiring boardmanufacturing method for forming a hole that penetrates through a boardhaving an electric conductor layer and forming the electric conductorlayer in the hole to make electrical connection, the print wiring boardmanufacturing method comprising the steps A) to C) of:

A) forming a hole that penetrates through the board with a drillfeatured in that a blade portion is formed at a distal end and a grooveis formed by one stripe on the body, and an occupying rate of a metal ata proximal end of the blade portion of the body is in the range of 40%to 80%;

B) forming an electric conductor layer in a hole; and

C) forming an electric conductor circuit on a top layer of the board.

Following the above step A), it is desirable to incorporate the desmearstep.

In addition, it is desirable that the distal end diameter of a drill inthe step (A) be equal to or smaller than 300 microns.

As a result of an utmost study of the Inventor et al, it was found thattwo problems occur when a drill diameter is reduced in size. One problemis associated with strength of the drill per se and the other problem isassociated with discharge property of shavings. By overcoming these twoproblems, even if the drill diameter is small in size, an opening of aboard is ensured, and, as a result, electric connectivity or reliabilityof the resultant printed wiring board is hardly lowered.

In a drill, a blade portion is formed at a distal end thereof, and agroove portion is formed at a body thereof. The distal end blade portionis rotated, thereby cutting a metal layer such as a copper foil and aresin impregnated with a core material such as a glass/epoxy resinconfiguring a board, and then, providing an opening on the board whileshavings are formed. In the body, a groove portion formed in a helicalshape is formed, and the shavings of the board that are shaped materialsare discharged by means of the distal end blade portion.

If the diameter of the drill becomes small in size, the body is reducedin thickness, and thus, there is a concern that the strength is lowered.Hole forming is precluded due to damage to a drill, and thus, electricalconnectivity or reliability has been lowered in a through hole having aconductor layer formed thereon. If a rate of the groove portion islowered and a rate of a core portion is increased in order to ensure thestrength of the drill, the discharge property of shavings may belowered. Therefore, a desired opening shape cannot be formed on theboard, and hole forming is precluded. Accordingly, in a through holehaving an electric conductor layer formed thereon, electricalconnectivity or reliability has been occasionally lowered due to afactor such as the presence of clogged shavings.

In addition, with respect to the tendency of these failures, when theuse frequency of a drill becomes high, a phenomenon that electricconnectivity or reliability is lowered further remarkably due to afactor such as drill wear and tear has easily occurred. As a result,hole forming is precluded; even if an electric conductor layer has beenformed in a hole, it lacks electric connection stability; or an amountof hole positional shift increases, thereby causing a positional shiftin forming a pattern of an electric conductor circuit in thepost-processing step.

As a result, electric connection or reliability has been occasionallylowered. In particular, when a reliability test has been carried outunder a heat cycle condition, opened-circuit or short-circuit hasoccasionally occurred at the number of cycles at an earlier stage,depending on the use frequency of the drill.

In drilling using a drill, in order to enhance drilling efficiency, aplurality of boards, for example, two or more boards are laminated oneach other, and the boards at the same site are drilled at the sametime. At the time of drilling, it is desired that the boards be drilledat the same position and in the same shape, without dependency on thedrilling shape or position precision regardless of the number of sheets.However, in the case of a small diameter drill, the drilled holes havenot been occasionally formed at the same position and in the same shape.In particular, a positional shift on a board positioned at the bottom ofthe boards becomes large. Further, when the use frequency becomes high,there has been an increasing tendency that the drilled holes are notformed at the same position and in the same shape. Therefore, dependingon the board, electrical connectivity or reliability has beenoccasionally easily lowered.

In order to form an opening while drilling a work piece, in a drillfeatured in that a blade portion has been formed at a distal end and agroove has been formed in a body, the strength of the drill is improved,and the discharge property of shavings is not precluded by using thedrill featured in that an occupying rate of a metal in cross section ofa proximal end of a blade tip of the body is in the range of 40% to 80%and a curvature radius relevant to an axial vertical direction of thedeepest portion of a groove at the proximal end is in the range of 1.50mm to 3.50 mm. If a through hole is provided on the board formed by thedrill, a hole shape failure or a positional shift hardly occurs, andelectrical connectivity and reliability are hardly lowered.

In addition, in the drill of the present application, smears are formedto be lesser than those in a conventional drill. Therefore, desmearprocessing can be carried out within a short period of time. This isbecause a desired drilling shape and discharge property of shavings areimproved at the time of drilling, thus reducing the degree of formingsmears. Therefore, deformation of a through hole due to a desmearprocess (forming of irregularities or waving due to excessive smearremoval) can be prevented, and the forming of a plating film of anelectric conductor layer is hardly precluded.

By being a drill featured in that an occupying rate of a metal in crosssection at a proximal end of a blade tip of a drill body is in the rangeof 40% to 80%, the discharge property of shavings is improved; holeforming is hardly precluded; and then, holes are easily formed in thesame shape. Therefore, even if an electric conductor layer has beenformed on a through hole formed on a board due to drilling,disconnection of the electric conductor layer hardly occurs. Thus,electric connectivity or reliability is hardly lowered.

In a drill featured in that an occupying rate of a metal in crosssection at a proximal end of a blade tip of a body is in the range of40% to 80%, the strength of the drill per se can be ensured; damage tothe drill (including damage to the drill that suddenly occurs) hardlyoccurs, and hole forming is hardly precluded. Therefore, while a drillis used during a desired number of shots (the desired number of shotsdenotes a predetermined number of shots when a drilled through hole isformed in accordance with the predetermined number of shots, andsubsequently, the drill is exchanged to form the through hole), damageto the drill hardly occurs when a through hole is formed on a board witha usual drill device. Asa result, a through hole is not precluded frombeing formed on the board, and electrical connectivity and reliabilityare hardly lowered regardless of the number of shots.

Even if a through hole has been formed by means of a drill of thepresent application while a plurality of boards, for example, two ormore boards are laminated on each other, a hole forming failure and ahole positional shift hardly occur. In this case, the hole formingfailure and the positional shift hardly occur regardless of a locationin which the boards are laminated on each other. As a result, even if anelectric conductor circuit has been formed on the board, a connectionfailure or the like between (a land including) an electric conductorcircuit and a through hole hardly occurs. As a result, electricalconnectivity and reliability are hardly lowered.

In addition, even if the drill use frequency (that denotes that throughholes are repeatedly formed on substrates by means of the same drillover 2000 drill shots or more, for example) becomes high, causing thewear and tear of the drill or the like, damage to the drill hardlyoccurs. In other words, the opening shape and positional shift of theboard hardly occurs. As a result, electrical connectivity andreliability is hardly lowered.

Further, even if a drill diameter is reduced in size (in particular,even if the drill diameter is reduced to be equal to or smaller than 300microns), hole forming is hardly precluded and a positional shift hardlyoccurs similarly. In particular, when a reliability test has beencarried out under a heat cycle condition, functional lowering caused bydisconnection or the like is hardly accelerated regardless of a drilluse frequency, a drilling condition, and a drill diameter.

In particular, in a drill diameter equal to or smaller than 150 microns,there occurs a case in which the degree of damage to a drillsignificantly appears. Thus, in a small diameter drill, it was foundthat there are improved an advantage at an occupying rate of a metal ata proximal end of a blade tip of a drill body, the discharge property ofshavings, and damage to a drill.

If the occupying rate of a metal in cross section at a proximal end of ablade tip of a drill body is less than 40%, the discharge property ofthe shavings is lowered. Therefore, the shavings are easily clogged inthe groove, whereby, when drilling has been done on the board,irregularities or deformations are likely to occur on an internal wallof a through hole. As a result, if an electric conductor is applied intothe through hole, the thickness of the electric conductor layer ishardly uniformed. Therefore, at a portion at which the electricalconductor layer becomes thin, disconnection is likely to occur, andthen, electric connectivity and reliability are lowered. In addition,the degree of forming smears may be increased.

If an occupying rate of a metal in cross section at a proximal end of ablade tip of a drill body exceeds 80%, the strength of a drill per se islowered, and then, damage to the drill is likely to occur when a throughhole is formed on a board. In addition, damage to the drill is likely tooccur before a desired number of shots has been reached, and deformationof the through hole is likely to occur if drilling is carried out on theboard in that state. As a result, if an electric conductor layer isapplied into the through hole, the thickness of the electric conductorlayer is hardly uniformed. Therefore, at a portion at which the electricconductor layer becomes thin, shirt-circuit or the like is likely tooccur, and electrical connectivity and reliability may be lowered.

In particular, it is desirable that an occupying rate of a metal incross section at a proximal end of a blade tip of a body be in the rangeof 40% to 80%. As a result of further utmost study of the Investor etal, it was found that damage to a drill is likely to occur at a distalend. Therefore, being the occupying rate of the metal ensures dischargeof the shavings formed at the distal end and the drill strength, andthus, damage to the drill hardly occurs. Further, assuming that a grooveis formed in one stripe (one discharge groove is provided with respectto a drill), the occupying rate of the metal is in the range of 40% to80% at its distal end. Thus, even if the diameter is reduced in size(this downsizing in diameter denotes that the drill diameter is equal toor smaller than 300 microns, in particular, that the drill diameter isequal to or smaller than 150 microns), the shape of a drilled throughhole is maintained, and the drill per se is hardly damaged.

A description will be given with respect to an occupying rate of a metalof a drill.

On a face formed by cutting a cross section of a proximal end of a bladetip of the drill, a metal formed in a round rod shape free from groove,as shown in FIG. 21 (A) is obtained as an occupying rate of 100%. Then,a metal occupying rate of the drill is defined by subtracting therefroman area ratio at which the metal in the region formed of a grooveportion has been cut. In general, a depth or width of the groove issubstantially uniform, and thus, it is recognized that the occupyingrate of metal in cross section is constant at a proximal end of a bladetip and a body center portion.

Drill of one-stripe groove type (refer to FIG. 21 (B))Metal ratio forming center portion: 100%Ratio at which groove portion is formed: X %Metal occupying rate of one-stripe type=100%-X %=A′%

In addition, by being a drill featured in that a curvature radius in anaxially vertical direction of the deepest portion of a groove at aproximal end of a blade tip is in the range of 1.50 mm to 3.50 mm, thedischarge property of shavings is improved; hole forming is hardlyprecluded, and the holes are easily formed in the same shape. Namely, bymeans of the distal end blade tip, a cut resin can be smoothlydischarged in the groove, and the rotation of drill is not precluded.Thus, an opening is formed on aboard in a desired shape. Therefore, evenif an electric conductor layer is formed at a through hole formed on theboard by means of a drill, disconnection of the electric conductor layeror the like hardly occurs, and thus, electric connectivity andreliability are hardly lowered. The deepest portion denotes a point Pthat is the closest to an axis center CC of the groove 20, as shown inFIG. 22 (A), FIG. 22 (B), and FIG. 22 (C).

In a drill featured in that a curvature radius in an axially verticaldirection of the deepest portion of a groove at a proximal end of ablade tip is less than 1.50, the shavings formed at the distal end bladeis hardly discharged smoothly in the groove. Thus, the shavings areeasily clogged in the groove, and damage to the drill easily occurs. Asa result, a shape failure or a positional shift of an drilled throughhole hardly occurs. Electrical connectivity and reliability are easilylowered. In addition, if the drill use frequency increases or if thedrill diameter is reduced in size, further, the shavings are easilyclogged in the groove, and the clogging failure is likely to appear.

In a drill featured in that a curvature radius in an axially verticaldirection of the deepest portion of a groove at a proximal end of ablade tip exceeds 3.50 mm, shavings are likely to wobble at a dischargeportion depending on the rotation frequency at the time of discharge ofthe shavings. Thus, the center axis of the drill may be displaced, andsuch displacement may cause a positional shift of the hole. Therefore,electric connectivity and reliability have been occasionally lowered.

In addition, in a drill featured in that a curvature radius exceeds 3.50microns, a distal end portion of a groove more easily arrives at thevicinity of a center portion of the groove. As a result, the strength ofthe drill per se is easily lowered; damage to the drill easily occurs;and a shape failure or a positional shift of a through hole to bedrilled easily occurs. Thus, electrical connectivity and reliability areeasily lowered. In particular, if the use frequency of the drillincreases or if the drill is reduced in diameter, the above failure islikely to occur.

With reference to FIG. 22 (A), a description will be given with respectto a curvature radius of a groove portion.

When a drill cut cross section is seen, an inverse value of thecurvature is taken to numerically represent its face in the curvature inthe deepest portion P of the groove 20, and the inverse number has beenrepresented as a curvature radius.

ΔS=RΔθ  (1)

ΔS: This indicates a length from P to P′.Δθ: This indicates an angle between CP and CP′.

From the equation (1), R=ΔS/Δθ is established.

In a drill featured in that an occupying rate of a metal in crosssection of a proximal end of a blade tip of a drill is in the range of40% to 80%, and a curvature radium in an axially vertical direction ofthe deepest portion of a groove at a proximal end of the blade tip is inthe range of 1.50 mm to 3.50 mm, even if the rotation frequency is setto be equal to or greater than 300 Krpm, damage to the drill hardlyoccurs, and then, shavings can be properly discharged. Namely, thereliability of an opening during processing can be enhanced. Inaddition, in other words, an opening can be drilled by means of a drilleven at a high speed rotation, and then, the number of openings insingle processing time can be increased, making it possible to enhanceproductivity.

A groove of a body may be the deepest at a distal end portion that is aproximal end of a blade tip; the groove may be shallow as it is distantfrom the distal end portion; or the depths of all the grooves may beequal to each other. The groove should be shallow in consideration ofthe discharge property and strength of shavings.

It is desirable that a metal forming a drill be composed of any of:tungsten carbide, a metal inevitably containing Co of 3 to 10 wt % andthe residual tungsten carbide; and metal C. These metals is high inhardness, and thus, even if the groove has been formed at a desiredratio, the missing or the like at the time of processing hardly occurs,and the desired metal occupying ratio and the groove curvature radius ofthe present invention can be formed.

Even if the boards are laminated on each other, and then, a through holeis formed, the axis in rotation becomes uniform, and thus, damage to thedrill is reduced, and a positional shift is reduced. Therefore, theproblem at the time of formation hardly occurs, and thus, electricalconnectivity and reliability are hardly lowered.

In addition, even if the use frequency of the drill becomes high, thewear and tear of the drill is also reduced. Thus, in a drill having adesired metal occupying rate or a groove curvature radius of the presentinvention, there are a few cases in which an opening deviates greatlyfrom a set value until the desired drill use frequency has beenobtained. Thus, a through hole formed on the board hardly causes a shapefailure or a positional shift. Therefore, electrical connectivity andreliability are hardly lowered.

In addition, in a re-ground drill as well, an occupying rate of a metalof the drill is in the range of 40% to 80%, and a curvature radius in anaxially vertical direction of the deepest portion of a groove at aproximal end of a blade tip is in the range of 1.50 mm to 3.50 mm,whereby it was found that the opening property of the board ismaintained, and a positional shift is prevented in a similar manner tothat of a new drill.

In a conventional drill, if a distal end diameter of the drill is equalto or smaller than 300 microns, the strength of the drill has not beensuccessfully maintained or a problem with discharge of shavings has beenlikely to occur.

With a drill according to the present application, featured in that anoccupying rate of a metal of the drill is in the range of 40% to 80% anda curvature radius of a distal end portion of a groove of a body is inthe range of 1.50 mm to 3.50 mm, these problems hardly occur. Therefore,a small diameter through hole can be formed and then, electricalconnectivity and reliability are easily obtained. In addition, even ifgaps (pitches) of the adjacent through holes are smaller thanconventional, a forming failure caused by a drill (for example, thisfailure denotes that a formed through hole is displaced moresignificantly than a designed value, such as positional shift orunstable pitch distance), thus making it possible to obtain a boardhaving its high density and fine pitches.

In the present invention, a printed wiring board manufacturing methodfor forming a hole penetrating through a board having an electricconductor layer and forming the electric conductor layer in the hole tomake electrical connection, the method comprising:

A) forming a hole that penetrates through the board in accordance with adrill featured in that a blade portion is formed at a distal end and agroove is formed by one stripe, and an occupying rate of a metal at aproximal end of the blade tip of the body is in the range of 40% to 80%;and a curvature radius in an axially vertical direction of a deepestportion of the groove is in the range of 1.50 to 3.50 mm;

B) forming an electric conductor layer in a hole; and

C) forming an electric conductor circuit on a top layer of the board.

Following the above step A), it is desirable to include a desmear step.

desmear can be carried out in accordance with either of a wettypedesmear (desmear processing carried out by immersion using achemical such as an acid or an oxidizing agent) or a dry type desmear(oxygen and nitrogen plasma processing or corona processing). In theseprocesses as well, desmear is reliably carried out within a short periodof time, as compared with a conventional drill. Therefore, the drilledthrough hole can be prevented from being deformed due to the step otherthan the drilling step, i.e., due to the desmear step.

It is desirable that the distal end diameter of the drill in the step A)be equal to or greater than 300 microns. In a drill according to thepresent application, featured in that an occupying rate of a metal incross section of a proximal end of a blade tip is in the range of 40% to80% and a curvature radius in an axially vertical direction of thedeepest portion of a groove at a proximal end of the blade tip is in therange of 1.50 mm to 3.50 mm, these problems hardly occurs. Therefore, asmall diameter through hole can be formed and then, electricalconnectivity and reliability are easily obtained. In addition, even ifgaps (pitches) of the adjacent through holes are smaller thanconventional, a forming failure caused by a drill (for example, thisfailure denotes that a formed through hole is displaced moresignificantly than a designed value, such as positional shift orunstable pitch distance), thus making it possible to obtain a boardhaving its high density and fine pitches.

A positional shift of a drilled through hole is reduced using a drillfeatured in that a torsion angle of a drill groove is in the range of 30degrees to 50 degrees. In other words, the hole forming precision isimproved. In addition, the shavings of the drill are properlydischarged, thus making it possible to obtain a printed wiring boardhaving its excellent electrical connectivity and reliability because theshavings do not preclude at the time of drilling. In addition, the wearand tear of the drill due to the use frequency can be restricted, thusmaking it possible to increase the use frequency more significantly thanconventional, and then, the precision and shape of a hole to be drilledis hardly lowered.

If shavings interfere at the time of drilling, a positional shift of ahole occurs, and then, irregularities are formed on an internal wall ofthe hole. Therefore, the lowering of electrical connectivity andreliability may occur. Shavings are likely to apply excessive stress tothe drill, and thus, the wear and tear of the drill is accelerated.

In the case where a torsion angle is less than 30 degrees or in the casewhere a torsion angle exceeds 50 degrees, shavings are hardlydischarged. Therefore, the shaving causes a positional shift of the holebecause they preclude drilling, and irregularities are formed on theinternal wall of the hole. Thus, electrical connectivity and reliabilityare lowered. The wear and tear of the drill is easily accelerated due tothe shavings that are hardly discharged. Therefore, the drilldeteriorates at an earlier use frequency.

It is further desirable that a torsion angle is in the range of 35degrees to 45 degrees. In this range, shavings are efficientlydischarged regardless of a drilling condition such as a rotationfrequency or a drill advancement speed. Therefore, a failure such as apositional shift of the hole or irregularities on the internal wall ofthe hole hardly occurs. In addition, the wear and tear of the drill isreduced, and thus, the drill can be used for a longer period. Thedrilled hole does not lower precision or the like.

A torsion angle indicates an angle at which a body forming a drill and agroove cross. That is, this torsion angle denotes an angle formed by aleading edge and a straight line parallel to a drill axis passingthrough one point on the edge.

It is desirable that a distal end angle of a blade portion of a distalend of a drill be in the range of 110 degrees to 150 degrees.

As long as the distal end angle is in the above range, a positionalshift hardly occurs, and a hole is formed in a desired shape. Even ifdrilling has been carried while boards are laminated in plurality, theholes are vertically formed similarly in the same shape. In addition,electrical connectivity and reliability is hardly lowered due to the usefrequency of the drill.

If the distal end angle of the distal end blade portion is less than 110degrees, irregularities are easily formed on the internal wall of thedrilled hole. If irregularities are subjected to desmear processing,such irregularities are further accelerated, and thus, theirregularities increases. After an electric conductor layer is appliedto the drilled hole, when a through hole is formed, a thickness of theelectric conductor layer fluctuates due to the irregularities.Therefore, electrical characteristics (such as impedance and throughhole internal resistance value) are lowered.

In addition, if the distal end angle of the distal end blade portionexceeds 150 degrees, the drilled hole is easily shifted from a desiredposition. In particular, when the boards are laminated each other inplurality, tendency of the positional shift further significantlyappears. Therefore, when a hole has been formed as a through hole,electrical connection with another electric conductor layer is lowered.In addition, when a reliability test is carried out, deteriorationstarts at an earlier stage.

It is more desirable that the distal end angle of the distal end bladeportion be in the range between 120 degrees and 140 degrees. In thisrange, even if an angle fluctuation has occurred, a hole deformation ora positional shift hardly occurs.

The distal end angle of the blade portion indicates an angle of a gap atwhich, when a drill is seen from a distal end, a metal portion formed byone blade is absent. This angle denotes an angle when a cutting blade isprojected in parallel to a face parallel to the axis of the drill.

It is desirable that an angle of a second release angle of a distal endblade portion be in the range of 30 degrees to 50 degrees.

As shown in FIG. 19 (A), a distal end release face of a drill accordingto the present invention is formed in a multi-staged face shape composedof a plurality of flat release faces, and then, first to fourth releasefaces that are flat faces from the cutting blade to the drill rotationdirection are sequentially disposed along a peripheral direction. Amongthem, it is desirable to set a release angle of the second release face(an angle formed by an axially vertical cross section and a release faceat the outer periphery corner) in the range of 30 degrees to 50 degrees.

It is desirable that a diameter of the body be equal to or smaller than300 microns.

Being that diameter has an advantage that hole position precision iseasily improved and a hole is formed in a desired shape, and thus, thelowering of electrical connectivity and reliability hardly occurs.

In particular, when using a drill having low rigidity and a diameterequal to or smaller than 150 microns, the metal occupying rate andgroove curvature of the present application is set, thereby making itpossible to enhance the use frequency. The lowering of electricalconnectivity and reliability hardly occurs.

In a so-called undercut drill, a neck narrowed in a cylindrical shape ina body may be formed. A portion from a distal end of this blade portionto the neck is referred to as a margin portion. It is desirable that ashaving discharge groove formed in the body be at the inside withrespect to an end of this margin portion. That is, it is preferable thatthe shaving discharge groove should not contact to the neck. Inparticular, it is desirable that the distance be present at the insideby 100 microns or more from an end part. In this manner, the shavingscan be properly discharged, and a stress is not applied, and thus, thelowering of the hole position precision and the shape of a hole formeddoes not occur.

A length of the margin portion indicates a distance from a distal end toa neck, i.e., a length obtained by subtracting a length of the neck froma length of the body. It is desirable that the length of the marginportion be in the range of 0.1 mm to 0.3 mm. In particular, in the casewhere the distal end outer diameter of the drill is equal to or smallerthan 200 microns, it is more desirable that the length of the marginportion be in the range of 0.1 mm to 0.3 mm.

If the length of the margin portion is less than 0.1 mm, a region formedby a groove for discharging shavings is reduced, and thus, a stress iseasily applied to a drill. Thus, the stress cannot be buffered, andtherefore, an occurrence frequency of drill bending or break and thelike increases. In addition, the hole position precision is occasionallylowered.

If the length of the margin portion exceeds 0.3 mm, the hole positionprecision is lowered.

An undercut type equipped with a neck is suitable to form a smalldiameter hole. Namely, a hole equal to or smaller than 400 microns canbe drilled. Further, it is preferable to drill a hole equal to orsmaller than 200 microns, in particular.

While the above description of the drill is given with respect to adrill of one groove type relevant to a groove, similar advantageouseffect can be attained with respect to a drill of two-groove type.

As shown in FIG. 36, a processing device 100 for drilling a printedwiring board in the present application is equipped with an X-Y table 90for placing a copper-plated laminate board or a multi-layered printedwiring board 60. The X-Y table 90 is equipped with a table drivemechanism 114 that can move to axes X and Y, respectively. In addition,the X-Y table is equipped with a spindle mechanism 106 for rotating adrill 10 and a spindle drive mechanism 112 for driving the spindlemechanism 106. A drill discharge groove formed in one stripe is fixed toeach of these spindles 106, and a penetration opening 66 is provided ona printed wiring board 60 at a rotation speed/drilling feed speed. It isdesirable that these rotation speeds be at least 100 Kprm. What is moredesirable is equal to or greater than 200 Kprm.

These table drive mechanism 114 and spindle drive mechanism 112 eachcarry out alignment of a precise position for driving or drilling inaccordance with a timing of drilling using a drill. Interlocking with acomputer 110 that precisely controls these drive mechanisms is made.Processing data 108 is inputted to the computer 110.

A material for the X-Y table 90 can be used as that generally used for aprocessing device. It is more desirable to use a material that is hardlyaffected by a heat at the time of processing. The board 60 placed on theX-Y table 90 may be one or may be subjected to drilling processing whilea plurality of boards, for example, two or more boards are laminated oneach other (for example, four boards are laminated on each other as suchan example.) The number of boards is properly adjusted in accordancewith a drill, boards, and the shape of a hole to be drilled.

In addition, it is desirable that a feed speed of these drills be atleast 30 inches per minute. It is more desirable that the speed be equalto or greater than 40 inches per minute. Productivity is ensured, andthe opening shape of the board is stabilized by the rotation speed andfeed speed described previously. Namely, board connectivity andreliability is hardly lowered.

As a drill 10 used for this spindle mechanism 106, it is desirable touse a drill of which a torsion angle of a discharge groove formed in onestripe in a body be in the range of 30 degrees to 50 degrees. Thus,shavings are efficiently discharged. In addition, even if a plurality ofboards are laminated on each other, a failure with forming a hole hardlyoccurs.

As a drill 10 used for this spindle mechanism 106, it is desirable touse a drill in which a groove is formed in one stripe in the distal endblade portion and body, the metal occupying rate at the proximal end ofthe blade tip of the body be in the range of 40% to 80%, and a curvatureradius in an axially vertical direction of the deepest portion of agroove at the proximal end be in the range of 1.50 mm to 3.50 mm. Thisis because the property of discharging shavings and preclusion offorming holes are prevented by these drills. In addition, even if aplurality of boards are laminated, a failure with forming holes hardlyoccurs.

The spindle mechanism 106 adjusts a drill rotation speed, and then, thespindle drive mechanism 112 described previously properly preciselycontrols a feed speed of a drill, drill elevation, or drill movement andthe like. Therefore, interlock with the computer 110 is made.

Drills may be used, each of which is equal to or smaller than 300microns in diameter. By means of these drills, small diameter drillingcan be carried out precisely.

The computer 110 that controls processing devices causes control of theX-Y table or spindle at the time of processing or drilling at apredetermined position, and occasionally, controls a drive timing of amechanism of these processing devices.

The processing device 100 in the present application is equipped with:an X-Y table 90 for placing one or two or more drilling printed wiringboard 60 to be laminated on each other; a spindle mechanism 106 equippedwith a drill 10 having a groove formed in one stripe; a mechanism 112,114 for driving the X-Y table 90 or spindle mechanism 106; and acomputer 110 that controls driving and drilling positioning operationsor the like.

As another mechanism, a mechanism for positioning a board is provided.This mechanisms include: a camera 102 for picking up as an image apositioning mark 61 on a board 60; an image processing unit 104 forimage-processing an image picked up by the camera 102; and a computer100 for calculating a position. A precise processing position iscalculated in accordance with the position of the positioning mark 61,driving the X-Y table 90 and the spindle mechanism 106 or the like.

In addition, a mechanism for counting the number of drilling shots maybe provided in order to grasp a drill exchange period. A temperaturecontrol unit may be provided in order to maintain the inside of theprocessing device at a constant temperature. In the processing device,it is desirable to provide an envelope in consideration of a safetyaspect of preventing damage to a human body due to drill breakage orscattering of shavings or a manufacturing aspect of preventing entry offoreign matter such as dust or controlling a temperature.

Advantageous Effect

A drill according to the present invention has sufficient strength, hasgood discharge property of shavings, and does not preclude the dischargeproperty of shavings. Drilled through holes are easily formed in thesame shape, and then, a shape failure or a positional shift hardlyoccurs. Thus, electrical connectivity and reliability of a through holeformed in a through hole are hardly lowered. The remaining amount ofsmear is reduced due to improvement of the discharge property ofshavings, thus making it possible to prevent deformation of a throughhole due to desmear.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view showing a drill according to an embodiment of thepresent invention.

FIG. 2 (A) is a front view when a distal end side of the drill shown inFIG. 1 is seen.

FIG. 2 (B) and FIG. 2 (C) are enlarged views each showing a distal endpart of the drill.

FIG. 3 is an illustrative view illustrating the steps of manufacturingthe drill.

FIG. 4 (A) is a side view showing a drill of a straight type.

FIG. 4 (B) is a side view showing a drill of an undercut type.

FIG. 5 is an illustrative view illustrating the steps of manufacturing aprinted wiring board.

FIG. 6 is an illustrative view illustrating drilling of a through holeinto a copper filed laminate board.

FIG. 7 is a chart showing an evaluation result of each of First Example1 and First Reference Example 1.

FIG. 8 is a chart showing an evaluation result of each of First Example2 and First Reference Example 2.

FIG. 9 is a chart showing an evaluation result of each of First Example3 and First Reference Example 3.

FIG. 10 is a chart showing an evaluation result of each of First Example4 and First Reference Example 4.

FIG. 11 is a chart showing an evaluation result of each of First Example5 and First Reference Example 5.

FIG. 12 is a chart showing an evaluation result of each of First Example6 and First Reference Example 6.

FIG. 13 is a chart showing an evaluation result of each of First Example7 and First Reference Example 7.

FIG. 14 is a chart showing an evaluation result of each of First Example8 and First Reference Example 8.

FIG. 15 is a chart showing an evaluation result of each of First Example9 and First Reference Example 9.

FIG. 16 is a chart showing a break result of each of First Example 9 andFirst Reference Example 9.

FIG. 17 is a chart showing an evaluation result of Comparative Example1.

FIG. 18 (A) is a side view showing a drill according to an embodiment ofthe present invention.

FIG. 18 (B) is a side view showing a drill of an undercut type.

FIG. 19 (A) is a front view when a distal end side of the drill is seen.

FIG. 19 (B) is an enlarged view showing a distal end part of the drill.

FIG. 19 (C) is a sectional view taken along the line C-C.

FIG. 19 (D) is an enlarged view showing a distal end part of the drill.

FIG. 20 is an illustrative view illustrating the steps of manufacturingthe drill.

FIG. 21 is an illustrative view illustrating an occupying rate of thedrill according to the present invention.

FIG. 22 is an illustrative view illustrating the deepest portion of adrill groove according to the present invention.

FIG. 23 is a chart showing an evaluation result of each of SecondExample 1 and Second Reference Example 1.

FIG. 24 is a chart showing an evaluation result of each of SecondExample 2 and Second Reference Example 2.

FIG. 25 is a chart showing an evaluation result of each of SecondExample 3 and Second Reference Example 3.

FIG. 26 is a chart showing an evaluation result of Second ModifiedExample 1.

FIG. 27 is a chart showing an evaluation result of Second ModifiedExample 2.

FIG. 28 is a chart showing an evaluation result of Second ModifiedExample 3.

FIG. 29 is a chart showing an evaluation result of Second ModifiedExample 4.

FIG. 30 is a chart showing an evaluation result of Second ModifiedExample 5.

FIG. 31 is a chart showing an evaluation result of each of SecondComparative Example 1 and Second Comparative Example 2.

FIG. 32 is a chart showing an evaluation result of the number of damagecheck shots of each of Second Examples 1 to Second Example 3 and SecondModified Example 1.

FIG. 33 is a chart showing an Example of the number of damage checkshots of each of Second Modified Examples 1 to Second Modified Example4.

FIG. 34 is a chart showing an Example of the number of damage checkshots of each of Second Modified Examples 5, Second Modified Example 1,and Second Comparative Example 2.

FIG. 35 is a photograph showing a sectional view of a drill according toSecond Example 1.

FIG. 36 is a block diagram depicting a drilling processing device of aprinted wiring board according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION First Example

Now, a first example of the present invention will be described withreference to the accompanying drawings.

(Drill)

First, the steps of manufacturing a drill according to the firstembodiment will be described with reference to FIG. 3.

1. Preparing Material for Drill

Metals for use in the drill according to the present invention includealloys including iron, cobalt, and nickel or the like. A column 50including these metals is prepared so as to be equal to or greater thana diameter of a shank of a drill (FIG. 3 (A)). It is more desirable touse a super-hard alloy.

2. Drill Processing

In the prepared column 50, grinding is carried out in order to form abody 40 of a drill (FIG. 3 (B)). Namely, grinding is carried out until adesired distal end outer diameter has been obtained. In this manner, ashank 12 and the body 40 of the drill are configured. At this time, inthe body, a drill may be formed in an undercut shape by forming a neck(a portion narrowed in a cylindrical shape) at a portion for the body,as preferred.

Next, in the body 40 of the drill, a shaving discharge groove 20 forshaving discharge is formed in e helical shape (FIG. 3 (C)). The groove20 is formed of one stripe. At this time, a torsion angle of a crossingpoint between the groove 20 and the body 40 is formed in a desiredshape. At this time, it is desired to set the angle in the range of 30degrees to 50 degrees. At this time, a gap between the grooves 20 and 20may be uniform or the gap between the grooves may be gradually changed.This gap is properly determined depending on a drilling diameter and amaterial or the like for drilling.

Next, a blade portion 30 that is a distal end part of the drill isprocessed (FIG. 3 (D)). Although the processing sequence is not limitedin particular, a first angle and a second release angle forming theblade portion are processed, and then, each of the groove portions isprocessed to be ground. Then, a respective portion called a releaseangle is processed in a planer shape or in a conical shape and the like.In this manner, a drill of one blade consisting of the blade portion 30,the body 40, and the shank 12 can be obtained such that a one-stripeshaving discharge groove 20 for discharging shavings has been formed atthe body 40.

FIG. 1 is a side view showing a drill 10; FIG. 2 (A) is a front viewwhen a distal end side of the drill is seen; and FIG. 2 (B) and FIG. 2(C) are enlarged views each showing a distal end part of the drill.

As shown in FIG. 1, a distal end diameter D1 of the blade portion 30 ofthe drill 10 is set to 0.115 mm and a diameter D2 of the shank 12 is setto 2 mm. A cutting blade length L1 is set to 1.8 mm; a body length L2 isset to 2.0 mm; a full length is set to 31.75 mm; a margin length L4 isset to 0.25 mm; and a relief length L5 is set to 1 mm. On the otherhand, a torsion angle θ1 of the shaving discharge groove 20 is set to 40degrees.

A groove width L6 shown in FIG. 2 (C) is set to 0.145 mm. A distal endangle θ2 shown in FIG. 2 (B) is set to 150 degrees.

As shown in FIG. 2 (A), a distal end release face of the drill is formedin a multi-staged face shape composed of a plurality of flat releasefaces. A first release face 32A, a second release face 32B, a thirdrelease face 32C, and a fourth release face 32D that are flat faces fromthe cutting blade 31 toward a drill rotation direction (in thecounterclockwise direction shown in the figure) are sequentiallydisposed along a peripheral direction. In addition, an opposite sidefirst release face 32E and an opposite side second release face 32F,which are also flat faces, are disposed in the vicinity of an axle. Asecond chamfer face 33 formed in a sectional arc shape is providedadjacent to the fourth release face 32D and the opposite side secondrelease face 32F. A release angle of the first release face 32A is setto 10 degrees and a release angle of the second release face 32B is setto 40 degrees.

(Drill Processing Method of Printed Wiring Board) 1. Copper FoiledLaminate Board

An insulation substrate opened by means of the drill according to thepresent invention can be used as long as it is obtained as an organicinsulation substrate. Specifically, it is desirable that such insulationsubstrate be a rigid (hard) laminate substrate selected from an alamidenon-woven cloth-epoxy resin substrate; a glass cloth epoxy resinsubstrate; an alamide non-woven cloth-polyimide substrate; a glass clothbis maleimide triadine resin substrate; a glass cloth polyphenyleneether resin substrate, FR-4, and FR-5, or alternatively, a flexiblesubstrate made of a polyethylene ether (PPE) film or polyimide (PI)film.

The thickness of the above insulation resin substrate is in the range of10 microns to 800 microns, is preferably in the range of 20 microns to400 microns, and is optimally in the range of 50 microns to 300 microns.This is because, if the thickness becomes smaller than these ranges, therigidity is lowered, and the substrate is difficult to handle; andconversely, if the thickness is too large, a small diameter through holeand an electric conductor layer are difficult to form.

The thickness of a copper foil of an insulation substrate is in therange of 5 microns to 50 microns, is preferably in the range of 8microns to 30 microns, and is further preferably in the range of 12microns to 25 microns. This is because, when a small diameter throughhole is provided in accordance with drill processing, if the thicknessis too small, a pattern is precluded from being formed, and conversely,if the thickness is too large, a fine pattern is difficult to be formedin accordance with etching.

A one-sided or double-sided cupper plated laminate board of thesesubstrates is prepared and used.

2. Processing Condition

In order to carry out processing using a drill 10, as shown in FIG. 6,an abutment board (bakelite board) 92 larger than a laminate board to beprocessed is placed on an X-Y table 90. Then, on the abutment board, oneor more one-sided or double-sided cupper plated laminate boards 60 arelaminated. Moreover, as preferred, on the cupper plated laminate board,a swelling agent is impregnated in acryl, and then, an entry sheet 94 isplaced such that a metal layer such as aluminum has been provided in atop layer, whereby processing may be carried out. At the time ofdrilling, the swelling agent in the entry sheet 94 serves as alubricating agent.

At this time, it is desirable to use a drill processing condition below.

Rotation frequency: 100 Krpm to 500 Krpm

Feed speed: 30 inches per minute to 200 inches per minute

Number of shots: 2000 shots or more

Here, if the rotation frequency is less than 100 Krpm, processing cannotbe efficiently carried out. On the other hand, if the rotation frequencyexceeds 500 Krpm, a service life is reduced by drill heating.

If the feed speed is less than 30 inches per minute, processing cannotbe efficiently carried out. On the other hand, the feed speed exceeds200 microns per minute, a drill burden increases, and breakage easilyoccurs. In particular, it is desirable that the rotation frequency be inthe range of 100 Krpm to 400 Krpm and the feed speed be in the range of40 inches per minute to 120 inches per minute from the viewpoint ofprocessing efficiency and drill service life.

On a drilled cupper plated laminate board, a through hole and a boardhaving formed thereon a land and an electric conductor circuit of thethrough hole are formed in accordance with a subtractive process or atenting technique.

Further, a board may be laminated in accordance with a press techniquein order to form a multi-layered board or multi-layering may be carriedout in accordance with an additive process while the board having thethrough hole formed thereon is used as a core board.

First Example 1 1. Preparing Material for Drill

A metal formed of an alloy such as tungsten, iron, and cobalt wasprepared. The metal was prepared as having been adjusted to a diameterof a processing device for thickening the metal to be larger than adrill diameter to be circularly formed and for rotating a drill.

2. Drill Processing

First, a portion forming a body of a drill is processed. In this manner,a shank and a body of the drill are formed. At this time, a distal endouter diameter of a blade portion for the body is adjusted to a presetdiameter. Then, a shaving discharge groove is formed in a one-stripeshape in order to discharge shavings. At this time, a torsion angle ofthe drill is set so as to be a predetermined angle.

Then, a first angle and a second release angle was formed in order toform one blade, and then, the drills of First Example 1 and FirstReference Example 1 shown below were produced through the steps or thelike of forming a respective release angle. In First Example 1, as shownin FIG. 4 (A), a drill of straight type with no undercut was used.

TABLE 1 List of items of First Example and First Reference Example 1Distal end angle of Second Distal end Torsion blade release outer Itemangle portion angle diameter Type First 30 110 40 degree 100 μm StraightExample 1-1 First 120 40 degree 100 μm Straight Example 1-2 First 130 40degree 100 μm Straight Example 1-3 First 140 40 degree 100 μm StraightExample 1-4 First 150 40 degree 100 μm Straight Example 1-5 First 90 40degree 100 μm Straight Reference Example 1-1 First 100 40 degree 100 μmStraight Reference Example 1-2 First 160 40 degree 100 μm StraightReference Example 1-3 First 170 40 degree 100 μm Straight ReferenceExample 1-4

3. Drilling Processing of Drill (1) Drill Processing

Four double-sided copper plated laminate boards 60 shown in FIG. 5 (A)(material: glass epoxy resin or polyimide resin: 200 microns inthickness of insulation layer 62; and 12 microns in thickness on oneside of a copper foil 64) were laminated on an X-Y table 90 for drillprocessing of a drill processing device (available from Hitachi Via Co.,Ltd. Model: ND-N series) as shown in FIG. 6. A disposal board (backupboard) 92 was placed at the lower side of the double-sided copper platedlaminate board 60. An entry sheet 94 for drill processing was placed atthe upper side of the double-sided copper plated laminate board 60.

In that state, the drilling of a drilling diameter of 100 microns wascarried out in the drill condition shown below. At this time, every timethe four laminate boards were processed, the number of drilling shotswas converted as one shot.

<Drill Processing Condition>

Rotation frequency: 160 Krpm

Feed speed: 40 inches per minute

Shape of use drill: Drill shown in Table 1

Number of evaluation shots: 3000 shots and 6000 shots

In this manner, a through hole 66 having a drilling diameter of 100microns was provided in the board 60 (refer to FIG. 5 (B)).

After drill processing, a desmear processing was applied to thedouble-sided copper plated laminate board by means of a per manganeseacid or the like.

4. Forming an Electric Conductor in a Through Hole

An electroless plating film 66 and an electrolytic plating film 68 weresequentially provided, and then, an electric conductor layer was formedon an internal wall of a through hole 66 and a top layer of a laminateboard (refer to FIG. 5 (C)). At this time, the plating was carried outunder the plating conditions below.

Electroless Plating [Electrolytic Copper Plating Water Solution]

NiSO₄: 0.003 mol/l Tartaric acid: 0.200 mol/lCopper sulfate: 0.030 mol/lNaOH: 0.050 mol/lα, α′-bipyridyl: 100 mg/lPolyethylene glycol: 0.10 g/l

[Electroless Plating Condition]

Immersion was carried out at a liquid temperature 50° C. for 40 minutes.

Electrolytic Plating [Electrolytic Copper Plating Water Solution]

Sulfuric acid: 160 g/lCopper sulfate: 77 g/lAdditive (available from Atotech Japan, Product name: Copperacid GL): 1ml/l

[Electrolytic Plating Condition]

Current density: 2 A/dm²Time: 30 minutes

Temperature: 25° C. 5. Forming Circuit

An electric conductor layer was formed, and then, an etching resist wasformed on the layer. Then, a wiring drawn mask was placed, and then,exposure/developing was carried out. In this manner, a through hole(including a land) and an electric conductor circuit was formed of theresist. Then, etching was applied to a resist-free portion by using asulfate-based etching solution or the like, and then, an etching resistwas released. In this manner, a through hole, a land of a through hole72, and an electric conductor circuit 74 were formed (refer to FIG. 5(D)).

6. Embedding Through Hole

Using a thermosetting resin or a photo-setting resin as an embeddingresin 76, the embedding of a through hole 72 was carried out inaccordance with printing (refer to FIG. 5 (E)). At this time, thisembedding may be carried out using a mask having a through hole portiondrilled thereon. An embedding resin is excessively formed with respectto the through hole; and semi-hardening or hardening was carried out.Then, grinding was carried out, and a board surface was smoothened. Inthis manner, the through hole was embedded, and the smoothened board wasobtained.

7. Forming Solder Resist Layer

A terminal serving as a portion for carrying out an electricalconductivity test was drilled on both sides of a board 60, and a solderresist 76 was formed (FIG. 5 (F)).

First Example 2

First Example 2 and First Reference Example 2 were substantiallyidentical to First Example 1, whereas drills used for drill processingwere as shown in Table 2.

TABLE 2 List of items of First Example 2 and First Reference Example 2Distal end angle of Second Distal end Torsion blade release outer Itemangle portion angle diameter Type First 35 110 40 degree 100 μm StraightExample 2-1 First 120 40 degree 100 μm Straight Example 2-2 First 130 40degree 100 μm Straight Example 2-3 First 140 40 degree 100 μm StraightExample 2-4 First 150 40 degree 100 μm Straight Example 2-5 First 90 40degree 100 μm Straight Reference Example 2-1 First 100 40 degree 100 μmStraight Reference Example 2-2 First 160 40 degree 100 μm StraightReference Example 2-3 First 170 40 degree 100 μm Straight ReferenceExample 2-4

First Example 3

First Example 3 and First Reference Example 3 were substantiallyidentical to First Example 1, whereas drills used for drill processingwere as shown in Table 3.

TABLE 3 List of items of First Example 3 and First Reference Example 3Distal end angle of Second Distal end Torsion blade release outer Itemangle portion angle diameter Type First 40 110 40 degree 100 μm StraightExample 3-1 First 120 40 degree 100 μm Straight Example 3-2 First 130 40degree 100 μm Straight Example 3-3 First 140 40 degree 100 μm StraightExample 3-4 First 150 40 degree 100 μm Straight Example 3-5 First 90 40degree 100 μm Straight Reference Example 3-1 First 100 40 degree 100 μmStraight Reference Example 3-2 First 160 40 degree 100 μm StraightReference Example 3-3 First 170 40 degree 100 μm Straight ReferenceExample 3-4

First Example 4

First Example 4 and First Reference Example 4 were substantiallyidentical to First Example 1, whereas drills used for drill processingwere as shown in Table 4.

TABLE 4 List of items of First Example 4 and First Reference Example 4Distal end angle of Second Distal end Torsion blade release outer Itemangle portion angle diameter Type First 45 110 40 degree 100 μm StraightExample 4-1 First 120 40 degree 100 μm Straight Example 4-2 First 130 40degree 100 μm Straight Example 4-3 First 140 40 degree 100 μm StraightExample 4-4 First 150 40 degree 100 μm Straight Example 4-5 First 90 40degree 100 μm Straight Reference Example 4-1 First 100 40 degree 100 μmStraight Reference Example 4-2 First 160 40 degree 100 μm StraightReference Example 4-3 First 170 40 degree 100 μm Straight ReferenceExample 4-4

First Example 5

First Example 5 and First Reference Example 5 were substantiallyidentical to First Example 1, whereas drills used for drill processingwere as shown in Table 5.

TABLE 5 List of items of First Example 5 and First Reference Example 5Distal end angle of Second Distal end Torsion blade release outer Itemangle portion angle diameter Type First 50 110 40 degree 100 μm StraightExample 5-1 First 120 40 degree 100 μm Straight Example 5-2 First 130 40degree 100 μm Straight Example 5-3 First 140 40 degree 100 μm StraightExample 5-4 First 150 40 degree 100 μm Straight Example 5-5 First 90 40degree 100 μm Straight Reference Example 5-1 First 100 40 degree 100 μmStraight Reference Example 5-2 First 160 40 degree 100 μm StraightReference Example 5-3 First 170 40 degree 100 μm Straight ReferenceExample 5-4

First Example 6

First Example 6 and First Reference Example 6 were substantiallyidentical to First Example 1, whereas drills used for drill processingwere of undercut type with a neck 42 shown in FIG. 4 (B), and also shownin Table 6.

TABLE 6 List of items of First Example 6 and First Reference Example 6Distal end angle of Second Distal end Torsion blade release outer Itemangle portion angle diameter Type First 40 110 40 degree 100 μm UndercutExample 6-1 First 120 40 degree 100 μm Undercut Example 6-2 First 130 40degree 100 μm Undercut Example 6-3 First 140 40 degree 100 μm UndercutExample 6-4 First 150 40 degree 100 μm Undercut Example 6-5 First 90 40degree 100 μm Undercut Reference Example 6-1 First 100 40 degree 100 μmUndercut Reference Example 6-2 First 160 40 degree 100 μm UndercutReference Example 6-3 First 170 40 degree 100 μm Undercut ReferenceExample 6-4

First Example 7

First Example 7 and First Reference Example 7 were substantiallyidentical to First Example 1, whereas drills used for drill processingwere as shown in Table 7.

TABLE 7 List of items of First Example 7 and First Reference Example 7Distal end angle of Second Distal end Torsion blade release outer Itemangle portion angle diameter Type First 40 120 30 degree 100 μm StraightExample 7-1 First 120 35 degree 100 μm Straight Example 7-2 First 120 40degree 100 μm Straight Example 7-3 First 120 45 degree 100 μm StraightExample 7-4 First 120 50 degree 100 μm Straight Example 7-5 First 120 20degree 100 μm Straight Reference Example 7-1 First 120 25 degree 100 μmStraight Reference Example 7-2 First 120 55 degree 100 μm StraightReference Example 7-3 First 120 60 degree 100 μm Straight ReferenceExample 7-4

First Example 8

First Example 8 and First Reference Example 8 were substantiallyidentical to First Example 1, whereas a drill used for drill processingis of undercut type, and drilling was carried out as shown in Table 8.

TABLE 8 List of items of First Example 8 and First Reference Example 8Distal end angle of Distal end Torsion blade Margin outer Item angleportion length diameter Type First 40 120 0.1 mm 100 μm Undercut Example8-1 First 120 0.15 mm  100 μm Undercut Example 8-2 First 120 0.2 mm 100μm Undercut Example 8-3 First 120 0.3 mm 100 μm Undercut Example 8-4First 120 0.4 mm 100 μm Undercut Example 8-5 First 120 0.5 mm 100 μmUndercut Example 8-6 First 120 0.025 mm  100 μm Undercut ReferenceExample 8-1 First 120 0.05 mm  100 μm Undercut Reference Example 8-2First 120 0.075 mm  100 μm Undercut Reference Example 8-3

First Example 9

First Example 9 and First Reference Example 9 were substantiallyidentical to First Example 1, whereas drills used for drill processinghad a distal end outer diameters as shown in Table 9.

In addition, in First Example 9, with respect to a drill whose distalend outer diameter is equal to or smaller than 100 microns, at the timeof drill processing, a similar evaluation was carried out using 2 or 3laminates of double-sided copper plated laminate boards.

TABLE 9 List of items of First Example 9 and First Reference Example 9Distal end angle of Second Distal end Torsion blade release outer Itemangle portion angle diameter Type First 40 120 30 degree 100 μm StraightExample 9-1 First 120 35 degree 150 μm Straight Example 9-2 First 120 40degree 200 μm Straight Example 9-3 First 120 45 degree 250 μm StraightExample 9-4 First 120 50 degree 300 μm Straight Example 9-5 First 120 20degree 350 μm Straight Example 9-6 First 120 25 degree  75 μm StraightExample 9-7 First 120 25 degree  50 μm Straight Example 9-8 First 120 55degree 400 μm Straight Reference Example 9-1 First 120 60 degree 500 μmStraight Reference Example 9-2

First Comparative Example

First Comparative Example was substantially identical to First Example1, whereas drills used for drill processing were as shown in Table 10.

TABLE 10 List of items of First Comparative Example Distal end Distalend Torsion angle of blade outer Item angle portion diameter Type FirstComparative 50 — 100 μm Straight Example 1 Two-blade First Comparative50 — 200 μm Straight Example 2 Two-blade First Comparative 25 100 100 μmStraight Example 3 First Comparative 110 100 μm Straight Example 4 FirstComparative 120 100 μm Straight Example 5 First Comparative 55 100 100μm Straight Example 6 First Comparative 110 100 μm Straight Example 7First Comparative 120 100 μm Straight Example 8

<Evaluation Items> (1) Precision of Hole Position

Evaluations were carried out with respect to positions of through holesformed in 3000 shots and 6000 shots. Namely, positional shift distancesof center points of through holes being formed at center portion with aland was compared.

◯: Within positional shift range of 35 micronsΔ: Within positional shift range of 50 micronsX: In excess of positional shift range of 50 microns

(2) Cross Section of Through Hole

Cross cutting of a cross section of a through hole in 3000 shots and6000 shots was carried out, and then, it was checked whether or notirregularities on a side face of an electric conductor layer existed.

◯: Maximum degree of irregularity of opening is within 8 microns.Δ: Maximum degree of irregularity of opening is within 10 microns.X: Maximum degree of irregularity of opening is in excess of 10 microns.

(3) Measuring Electric Conductivity of Through Hole

It was checked whether or not there exists electric conductivity on bothsides of a through hole in 3000 shots and 6000 shots.

◯: Electrically conductiveX: Not electrically conductive

(4) Reliability Test

While a heat cycle test (125° C. per 3 minutes <=>−65° C. per 3 minutes)was defined as one cycle, the test was repeated until the number ofcycles in which a conductivity failure was confirmed. Then, areliability evaluation was carried out using an electrical conductivitytest such as a disconnection test. The maximum number of cycles was3000. The an electric conductivity test was carried out every 1500cycles, 2000 cycles, and 3000 cycles.

With respect to a case in which 2500 cycles were cleared, no problemoccurred in actual use.

(5) Drill Breakage Evaluation

With respect to First Example 9 and First Comparative Example 9, thepresence or absence of drill breakages in 1000 shots, 3000 shots, and6000 shots (◯: No breakage X: Breakage occurs) was evaluated. Inaddition, with respect to a case in which a distal end outer diameter ofa drill in First Example 9 is equal to or smaller than 100 microns, asimilar evaluation was carried out with respect to a case in which thenumber of laminates was 3 or 2.

FIG. 7 is a chart showing an evaluation result of each of First Example1 and First Reference Example 1; FIG. 8 is a chart showing an evaluationresult of each of First Example 2 and First Reference Example 2; FIG. 9is a chart showing an evaluation result of each of First Example 3 andFirst Reference Example 3; FIG. 10 is a chart showing an evaluationresult of each of First Example 4 and First Reference Example 4; FIG. 11is a chart showing an evaluation result of each of First Example 5 andFirst Reference Example 5; FIG. 12 is a chart showing an evaluationresult of each of First Example 6 and First Reference Example 6; FIG. 13is a chart showing an evaluation result of each of First Example 7 andFirst Reference Example 7; FIG. 14 is a chart showing an evaluationresult of each of First Example 8 and First Reference Example 8; FIG. 15is a chart showing an evaluation result of each of First Example 9 andFirst Reference Example 9; FIG. 16 is a chart showing a break result ofeach of First Example 9 and First Reference Example 9; and FIG. 17 is achart showing an evaluation result of Comparative Example 1.

From the evaluation results described above, as long as a torsion angleof a shaving discharge groove of a drill is in the range of 30 degreesto 50 degrees, it is found that a positional shift of a through holedrilled is small in size. In addition, it was clarified that the numberof usable shots can be extended and that the drilled hole hardly lowersthe precision and shape.

In the case where the torsion angle is less then 30 degrees or in thecase where the torsion angle exceeds 50 degrees, the electricconnectivity and reliability may be lowered. In addition, it was foundthat a drill deteriorates with a small number of shots used.

It is further desirable that the torsion angle be in the range of 35degrees to 45 degrees. In this range, it is possible to use a drill foran extended period of time, and the lowering of precision of the drilledhole does not occur.

It is desirable that a distal end angle of a distal end blade portion bein the range of 110 degrees to 150 degrees. In this range, a positionalshift hardly occurs, and the drilled hole is also formed in a desiredshape. In addition, even if the number of shots with a drill increases,electric connectivity and reliability of a through hole are hardlylowered.

If the distal end angle of the distal end blade portion is less than 110degrees, the electrical characteristics and reliability are lowered. Onthe other hand, if the distal end angle of the distal end blade portionexceeds 150 degrees, the drilled hole is easily shifted from a desiredposition. Therefore, when a hole has been formed as a through hole, theelectrical connection with other conductor layer is lowered. Inaddition, when a reliability test is carried out, deterioration startsat an earlier stage.

In particular, as long as the distal end angle of the distal end bladeportion is in the range between 120 degrees to 140 degrees, it was foundthat a positional shift hardly occurs. In addition, in the case where asecond release angle of the distal end blade portion was in the rangefrom 30 degrees to 50 degrees, it was found that reliability was notlowered.

In the case where a distal end outer diameter of a drill is in the rangebetween 100 microns to 350 microns, it is possible to say that nobreakage occurs and a printed wiring board is not affected so much inuse. The drill could be used without any limitation to the number oflaminates in particular. In the case where the outer diameter is lessthan 100 microns, a frequency of an occurrence of breakage increased.However, it was successfully verified that the drill was usable even ina large number of shots by changing a processing condition such as acondition for a limited number of laminates.

Second Example

Second Example of the present invention will be described below withreference to the accompanying drawings.

(Drill)

First, with reference to FIG. 20, a description will be given withrespect to the steps of manufacturing a drill according to SecondExample 1.

1. Preparing Material for Drill

Metals for use in a drill according to the present invention consistmainly of tungsten carbide and alloys including iron, cobalt, and nickelor the like. A column 50 including these metals is prepared so as to beequal to or greater than a diameter of a shank of the drill (FIG. 20(A)). In particular, it is more desirable to use a tungsten carbideserving as a hard metal.

2. Drill Processing

In the metal of the thus prepared column 50, grinding is carried out inorder to form a body 40 of a drill (FIG. 20 (B)). Namely, grinding iscarried out until a diameter of a desired body has been obtained. Ingeneral, a drill of a straight type is obtained. At this time, in thebody, an undercut shaped drill may be obtained such that a recessedportion has been formed partly of the body, as preferred.

In this manner, a shank 12 and the body 40 of the drill are configured.

Next, a shaving discharge grove 20 is formed in the body 40 of the drill(FIG. 20 (C)). The groove is formed in one stripe. At this time, atorsion angle of a crossing point between the groove 20 and the body 40is set at a desired angle. At this time, it is desirable that the anglebe set in the range of 30 degrees to 50 degrees.

At this time, the gap between grooves 20 may be uniform or the groovegap may be gradually changed. In addition, the drill may be of type suchthat the depth of the groove sequentially shallows toward the bodydirection of the drill or may be equal in depth. In the presentembodiment, the drill, hat the depth of the groove sequentiallyshallows, was processed and produced. This can be properly determineddepending on a drilling diameter or a drilling material and the like.

Next, a blade portion 30 that is a distal end part of the drill isprocessed (FIG. 20 (D)). With respect to the processing sequences,although not limited in particular, the first angle and the secondrelease angle forming the blade portion are processed, and then, each ofthe groove portions is ground and processed. Then, a portion called arespective release angle is processed in a planar shape or in a conicalshape and the like. In this manner, a one-stripe groove consisting ofthe blade portion 30, the body 40, and the shank 12, the groove beingadapted to discharge shavings, is formed in the body, whereby aone-blade drill can be obtained.

FIG. 18 (A) is a side view showing a drill 10. FIG. 19 (A) is a frontview when a distal end side of the drill is seen; FIG. 19 (B) is anenlarged view showing a distal end part of the drill; FIG. 19 (C) is asectional view taken along the line C-C in FIG. 19(B); and FIG. 19 (D)is an enlarged view showing a distal end part of the drill. FIG. 35 is aphotograph showing a cross section of the drill. FIG. 18 (C) is a sideview showing a drill of an undercut type.

As shown in FIG. 18, the distal end diameter D1 of the blade portion 30of a drill 10 is set to 0.115 mm and the diameter D2 of the shank 12 isset to 2 mm. A cutting blade length L1 is set to 1.8 mm; a body lengthL2 is set to 2.0 mm; and a full length L3 is set to 31.75 mm. On theother hand, a torsion angle θ1 of the shaving discharge groove 20 is setto 40 degrees. The groove width L6 shown in FIG. 19 (D) is set to 0.145mm. A distal end angle θ2 shown in FIG. 19 (B) is set to 150 degrees.

As shown in FIG. 19 (A), a distal end release face of the drill isformed in a multi-staged face shape composed of a plurality of flatrelease faces. A first release face 32A, a second release face 32B, athird release face 32C, and a fourth release face 32D that are flatfaces are sequentially disposed along a peripheral direction from acutting blade 31 toward a drill rotation direction (in thecounterclockwise direction in the figure). In addition, an opposite sidefirst release face 32E and an opposite side release face 32F that areflat faces are disposed in the vicinity of an axle. A second chamberface 33 formed in a sectional substantial arc shape is provide adjacentto the fourth release face 32D and the opposite side second release face32F. A release angle of the first release face 32A is set to 10 degreesand a release angle of the second release face 32B is set to 40 degrees.

As shown in FIG. 19 (C), across section of a proximal part of a bladetip was 69.77% in metal occupying rate. In addition, a curvature radiusin an axially vertical direction at the deepest part P (a site that isthe closest to an axle) of a proximal end of the formed groove 20 was2.95 mm.

(Drill Processing Method of Printed Wiring Board) 1. Copper PlatedLaminate Board

An insulation substrate opened by the drill according to the presentinvention can be used as long as it is obtained as an organic insulationsubstrate. Specifically, it is desirable that such insulation substratebe a rigid (hard) laminate substrate selected from an alamide non-wovencloth-epoxy resin substrate; a glass cloth epoxy resin substrate; analamide non-woven cloth-polyimide substrate; a glass cloth bis maleimidetriadine resin substrate; a glass cloth polyphenylene ether resinsubstrate, FR-4, and FR-5, or alternatively, a flexible substrate madeof a polyethylene ether (PPE) film or polyimide (PI) film.

The thickness of the above insulation resin substrate is in the range of10 microns to 800 microns, is preferably in the range of 20 microns to400 microns, and is optimally in the range of 50 microns to 300 microns.This is because, if the thickness becomes smaller than these ranges, therigidity is lowered, and the substrate is difficult to handle; andconversely, if the thickness is too large, a small diameter through holeand an electric conductor layer are difficult to be formed.

The thickness of a copper foil of an insulation substrate is in therange of 5 microns to 50 microns, is preferably in the range of 8microns to 30 microns, and is further preferably in the range of 12microns to 25 microns. This is because, when a small diameter throughhole is provided in accordance with drill processing, if the thicknessis too small, the pattern is precluded from being formed, andconversely, if the thickness is too large, a fine pattern is hardlyformed in accordance with etching. A one-sided or double-sided cupperplated laminate board of these substrates is prepared and used.

2. Processing Condition

Processing condition is the same as described in First Example.

At this time, it is desirable to use a drill processing condition below.

Rotation frequency: 100 Krpm to 500 Krpm

Feed speed: 30 inches per minute to 200 inches per minute

Number of shots: It is desirable to use as much as 3000 shots or more.

Here, if the rotation frequency is less than 100 Krpm, processing cannotbe efficiently carried out. On the other hand, if the rotation frequencyexceeds 500 Krpm, it increases the probability that a service life isreduced by drill heating.

If the feed speed is less than 30 inches per minute, processing cannotbe efficiently carried out. On the other hand, the feed speed exceeds200 inches per minute, a drill burden increases, and breakage easilyoccurs. In particular, it is desirable that the rotation frequency be inthe range of 200 Krpm to 400 Krpm and the feed speed be in the range of40 inches per minute to 120 inches per minute. This condition is moredesirable from the viewpoint of processing efficiency of a through holeand a service life of the drill. In addition, a failure in forming thethrough hole is also a processing condition that most hardly occurs.

On a drilled cupper plated laminate board, a through hole and a boardhaving formed thereon a land and an electric conductor circuit of thethrough hole are formed in accordance with a subtractive process or atenting.

Further, a board may be laminated in accordance with a press techniquein order to form a multi-layered board or multi-layering may be carriedout in accordance with an additive process while the board having thethrough hole formed thereon is used as a core board.

Second Example 1 1. Preparing Material for Drill

A metal formed with an alloy consisting mainly of tungsten carbide andalso metals such as cobalt was prepared. The prepared metal was adjustedto a diameter of a processing device for thickening the metal to belarger than a drill diameter to be circularly formed and for rotating adrill.

2. Drill Processing

First, a portion forming a body of a drill is processed. In this manner,a shank and a body part of the drill are formed. At this time, adiameter of the body is adjusted to a preset diameter. In this case, thedrill diameter is set so as to be 100 +/−10 microns.

Then, a groove is formed in a one-stripe shape so as to dischargeshavings. At this time, a torsion angle of the drill is set so as to bea preset angle. In this Second Example, the torsion angle is set to 40degrees. Then, in order to form one blade, a first angle and a secondrelease angle are formed, and then, the steps of forming a respectiverelease angle are carried out. At this time, with respect to a metaloccupying rate in a proximal end of a blade tip of the body and acurvature radius of the thus formed groove, drill processing was carriedout under a condition as shown in Table 11.

Table of items of Second Example and Second Reference Example

TABLE 11 Metal Curvature occupying radius of Drill Item rate groovediameter Type Second 69.8 2.95 100 μm Straight Example 1-1 Second 69.81.50 100 μm Straight Example 1-2 Second 69.8 3.50 100 μm StraightExample 1-3 Second 69.8 1.40 100 μm Straight Reference Example 1-1Second 69.8 3.60 100 μm Straight Reference Example 1-2

3. Drilling Processing of Drill Drill Processing

As in First Example described above with reference to FIG. 5 (A), fourdouble-sided copper plated laminate boards 60 (material: glass epoxyresin or polyimide resin; 200 microns in thickness of insulation layer62; and 12 microns in thickness of copper foil 64 on one side) werelaminated on an X-Y table 90 for drill processing of a drill processingdevice (available from Hitachi Via Co., Ltd. Model: ND-N series) asshown in FIG. 6. A disposal board (backup board) 92 was placed at thelower side of the double-sided copper plated laminate board. An entrysheet 94 for drill processing was placed.

In that state, the drilling of a drilling diameter of 100 microns wascarried out in the drill condition shown below. At this time, every timethe four laminate boards were processed, the number of drilling shotswas converted as one shot.

<Drill Processing Condition>

Rotation frequency: 300 Krpm

Feed speed: 40 inches per minute

Shape of use drill: Drill shown in Table 11

Number of evaluation shots: 1500 shots, 3000 shots, 4500 shots, and 6000shots

In this manner, a through hole 66 having a drilling diameter of 100microns was provided in the board 60 (FIG. 5 (B)).

After drill processing, a desmear processing was applied to thedouble-sided copper plated laminate board for 5 minutes by means of aper manganese acid.

4. Forming Electric Conductor in Through Hole

An electroless plating film 66 and an electrolytic plating film 68 weresequentially provided, and then, an electric conductor layer was formedon an internal wall of a through hole 66 and a top layer of a laminateboard (FIG. 5 (C)). At this time, plating was carried out under theplating condition similar to that in First Example.

5. Forming Circuit

A through hole 72, a land of a through hole 72, and an electricconductor circuit 74 were formed in the same manner as in First Example(FIG. 5 (D)).

6. Embedding Through Hole

Using a thermosetting resin or a photo-setting resin as an embeddingresin 76, the embedding of a through hole 72 was carried out inaccordance with printing in the same manner as in First Example (FIG. 5(E)).

7. Forming Solder Resist Layer

A terminal serving as a portion for carrying out an electricalconductivity test was drilled on both sides of a board 60, and a solderresist 76 was formed (FIG. 5 (F)).

Second Example 2

Table 12 shows a list of items in Second Example 2. In Second Example 2,a metal occupying rate was set to 40%, that is a lower limit.

TABLE 12 Metal Curvature occupying radius of Drill Item rate groovediameter Type Second 40 2.95 100 μm Straight Example 2-1 Second 40 1.50100 μm Straight Example 2-2 Second 40 3.50 100 μm Straight Example 2-3Second 40 1.40 100 μm Straight Reference Example 2-1 Second 40 3.60 100μm Straight Reference Example 2-2

Second Example 3

Table 13 shows a list of items of Second Example 3. In Second Example 3,a metal occupying rate was set to 80%, that is an upper limit.

TABLE 13 Metal Curvature occupying radius of Drill Item rate groovediameter Type Second 80 2.95 100 μm Straight Example 3-1 Second 80 1.50100 μm Straight Example 3-2 Second 80 3.50 100 μm Straight Example 3-3Second 80 1.40 100 μm Straight Reference Example 3-1 Second 80 3.60 100μm Straight Reference Example 3-2

Second Modified Example 1

Table 14 shows a list of items of Second Modified Example 1. SecondModified Example 1 was different from Second Example 1 in the drilldiameter, whereas a metal occupying rate was set to 80%, that is anupper limit.

TABLE 14 Metal Curvature occupying radius of Drill Item rate groovediameter Type Second 80 1.50 150 μm Straight Modified Example 1-1 Second80 1.50 250 μm Straight Modified Example 1-2 Second 80 1.50 300 μmStraight Modified Example 1-3 Second 80 1.50 350 μm Straight ModifiedExample 1-4 Second 80 3.50 100 μm Straight Modified Example 1-5 Second80 3.50 250 μm Straight Modified Example 1-6 Second 80 3.50 300 μmStraight Modified Example 1-7 Second 80 3.50 350 μm Straight ModifiedExample 1-8

Second Modified Example 2

Table 15 shows a list of items of Second Modified Example 2. SecondModified Example 2 was different from Second Example 1 in the drilldiameter, whereas a metal occupying rate was set to 40%, that is a lowerlimit.

TABLE 15 Metal Curvature occupying radius of Drill Item rate groovediameter Type Second 40 1.50 150 μm Straight Modified Example 2-1 Second40 1.50 250 μm Straight Modified Example 2-2 Second 40 1.50 300 μmStraight Modified Example 2-3 Second 40 1.50 350 μm Straight ModifiedExample 2-4 Second 40 3.50 100 μm Straight Modified Example 2-5 Second40 3.50 250 μm Straight Modified Example 2-6 Second 40 3.50 300 μmStraight Modified Example 2-7 Second 40 3.50 350 μm Straight ModifiedExample 2-8

Second Modified Example 3

Table 16 shows a list of items of Second Modified Example 3. SecondModified Example 3 was different from Second Example 1 in the drilldiameter, whereas a metal occupying rate was set to 80%, that is anupper limit.

TABLE 16 Metal Curvature occupying radius of Drill Item rate groovediameter Type Second 80 1.50 150 μm Straight Modified Example 3-1 Second80 1.50 250 μm Straight Modified Example 3-2 Second 80 1.50 300 μmStraight Modified Example 3-3 Second 80 1.50 350 μm Straight ModifiedExample 3-4 Second 80 3.50 100 μm Straight Modified Example 3-5 Second80 3.50 250 μm Straight Modified Example 3-6 Second 80 3.50 300 μmStraight Modified Example 3-7 Second 80 3.50 350 μm Straight ModifiedExample 3-8

Second Modified Example 4

Table 17 shows a list of items of Second Modified Example 4. SecondModified Example 4 was similar to Second Modified Example 2, whereasdrills of an undercut type were used as a drill.

TABLE 17 Metal Curvature occupying radius of Drill Item rate groovediameter Type Second 40 1.50 150 μm Undercut Modified Example 4-1 Second40 1.50 250 μm Undercut Modified Example 4-2 Second 40 1.50 300 μmUndercut Modified Example 4-3 Second 40 1.50 350 μm Undercut ModifiedExample 4-4 Second 40 3.50 100 μm Undercut Modified Example 4-5 Second40 3.50 250 μm Undercut Modified Example 4-6 Second 40 3.50 300 μmUndercut Modified Example 4-7 Second 40 3.50 350 μm Undercut ModifiedExample 4-8

Second Modified Example 5

Table 18 shows a list of items of Second Modified Example 5. SecondModified Example 5 was similar to Second Example 3, whereas a drill ofan undercut type was used as a drill.

TABLE 18 Metal Curvature occupying radius of Drill Item rate groovediameter Type Second 80 1.50 150 μm Undercut Modified Example 5-1 Second80 1.50 250 μm Undercut Modified Example 5-2 Second 80 1.50 300 μmUndercut Modified Example 5-3 Second 80 1.50 350 μm Undercut ModifiedExample 5-4 Second 80 3.50 100 μm Undercut Modified Example 5-5 Second80 3.50 250 μm Undercut Modified Example 5-6 Second 80 3.50 300 μmUndercut Modified Example 5-7 Second 80 3.50 350 μm Undercut ModifiedExample 5-8

Second Comparative Example 1

Table 19 shows a list of items of Second Comparative Example 1. InSecond Comparative Example 1, a metal occupying rate was set to 38.9%,and drills having a distal end diameter of 100 microns were used.

TABLE 19 Metal Curvature occupying radius of Drill Item rate groovediameter Type Second 38.9 1.34 100 μm Straight Comparative Example 1-1Second 38.9 1.49 100 μm Straight Comparative Example 1-2 Second 38.92.23 100 μm Straight Comparative Example 1-3 Second 38.9 3.21 100 μmStraight comparative Example 1-4 Second 38.9 3.71 100 μm StraightComparative Example 1-5

Second Comparative Example 2

Table 20 shows a list of items of Second Comparative Example 2. InSecond Comparative Example 2, a metal occupying rate was set to 81.2%,and drills having a distal end diameter of 100 microns were used.

TABLE 20 Metal Curvature occupying radius of Drill Item rate groovediameter Type Second 81.2 1.34 100 μm Straight Comparative Example 2-1Second 81.2 1.49 100 μm Straight Comparative Example 2-2 Second 81.22.23 100 μm Straight Comparative Example 2-3 Second 81.2 3.21 100 μmStraight comparative Example 2-4 Second 81.2 3.71 100 μm StraightComparative Example 2-5

<Evaluation Items> (1) Drill Damage Verification Test

In drills produced in Second Example, Second Reference Example, SecondModified Example, and Second Comparative Example, verification wascarried out with respect to the number of shots when damage to drillswas found. The results are shown in FIG. 32 to FIG. 34.

(2) Precision of Hole Position

Evaluations were carried out with respect to positions of through holesformed in 3000 shots and 6000 shots. Namely, a positional shift distanceof the center points of the through holes being formed at a centerportion with a land were compared.

A board positioned at the lowest part of the laminated boards was usedfor measurement. Length of the hole positions of 30 sites werearbitrarily measured. Evaluations were carried out in accordance with aratio that exceeds the positional shift range of 50 microns.

◯: Equal to or smaller than 3%Δ: Equal to or smaller than 5%

X: Over 5% (3) Cross Section of Through Hole

After desmear process in 3000 shots and 6000 shots in number, thecrosscutting of a cross section of a through hole on a substrate wascarried out, and the relevant cross section was observed. A boardpositioned at the lowest part of the laminated boards was used formeasurement. A total of 5 sites were observed, and the presence orabsence of smear residue was observed.

◯: No smearX: With smear residue

(4) Electric Conductivity Measurement of Through Hole

The presence or absence of electric conductivity at 3000 shots and 6000shots in number was verified.

◯: Electrically conductiveX: Not electrically conductive

(5) Reliability Test

A heat cycle test (125° C. per 3 minutes <=>−65° C. per 3 minutes) wasrepeatedly carried out until the number of cycles was reached such thatan electric conductivity failure is found, and reliability evaluationwas carried out through an electric conductivity test such as adisconnection test. A maximum number of cycles was 4000. An electricconductivity test was carried out every 1000 cycles such as 1000 cycles,2000 cycles, 3000 cycles, and 4000 cycles.

With respect to a case in which 3000 cycles were cleared, no problemoccurred in actual use. FIG. 23 to FIG. 31 show evaluation results ofSecond

Example, Second Reference Example, and Second Comparative Example. Fromthe above evaluation results, as long as a metal occupying rate of adrill was in the range of 40% to 80%, and a curvature radius of a distalend portion of a groove in a body was in the range of 1.50 mm to 3.50mm, it was found that the precision of the hole position is not lowered,and no problem such as smear residues occurs, and electric conductivityreliability is not lowered. In addition, it was clarified that theusable number of shots in a drill can be extended.

On the other hand, in the case where an occupying rate of a metal incross section at a proximal end of a blade tip in a drill body was lessthan 40% or in excess of 80%, it was found that the drill is easilydamaged, and the electric connectivity and reliability of the drilledthrough hole are lowered. On the other hand, in a drill featured in thata curvature radius in an axially vertical direction of the deepestportion of a groove is less than 1.50, a shape failure or a positionalshift of a drilled through hole is likely to occur, and the electricconnectivity and reliability is easily lowered. Similarly, in a drillfeatured in that a curvature radius exceeds 3.50 mm, it was found that ahole positional shift is easily induced and the electric connectivityand reliability is easily lowered.

INDUSTRIAL APPLICABILITY

While First Example and Second Example described above have shown anexample of using a drill for drilling a copper plated laminate board fora printed wiring board, the drill according to the present applicationcan be suitably used for drilling a laminate between a variety of resinsand a metal.

1. A printed wiring board manufacturing method for forming a holepenetrating through a board having an electric conductor layer andforming the electric conductor layer in the hole to make electricalconnection, the method comprising: forming a hole that penetratesthrough the board in accordance with a drill featured in that a bladeportion is formed at a distal end and a groove is formed by one stripe,and an occupying rate of a metal at a proximal end of the blade tip ofthe body is in the range of 40% to 80%; and a curvature radius in anaxially vertical direction of a deepest portion of the groove is in therange of 1.50 to 3.50 mm; forming an electric conductor layer in a hole;and forming an electric conductor circuit on a top layer of the board.2. The printed wiring board manufacturing method according to claim 1,wherein the step of carrying out desmear processing is carried out afterthe hole forming step.
 3. The printed wiring board manufacturing methodaccording to claim 1, wherein a distal end diameter of a drill in thehole forming step is equal to or smaller than 300 microns.
 4. Theprinted wiring board manufacturing method according to claim 1, whereina torsion angle of the drill is in the range of 30 degrees to 50degrees.
 5. A printed wiring board manufacturing method for forming ahole penetrating through a board having an electric conductor layer andforming the electric conductor layer in the hole to make electricalconnection, the method comprising: forming an opening that penetrates aboard by means of a drill featured in that a shaving discharge groove isformed in a one-stripe shape at a body and a torsion angle of theshaving discharge groove is in the range of 30 degrees to 50 degrees.forming an electric conductor layer in a hole; and forming an electricconductor circuit in a top layer of the substrate.
 6. The printed wiringboard manufacturing method as claimed in claim 5, wherein, in the drill,an occupying rate of a metal at the proximal end of the blade tip of thebody is in the range of 40% to 80%, and a curvature radius in an axiallyvertical direction of a deepest portion of a groove at the proximal endis in the range of 1.50 mm to 3.50 mm.
 7. The printed wiring boardmanufacturing method according to claim 2, wherein a distal end diameterof a drill in the hole forming step is equal to or smaller than 300microns.